using System;
using System.Collections.Generic;
using System.Globalization;
using System.Net.Http;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Threading;
using System.Threading.Tasks;
using Jellyfin.Plugin.Floatplane.Configuration;
using Microsoft.Extensions.Logging;

namespace Jellyfin.Plugin.Floatplane.Api;

/// <summary>
/// OAuth 2.0 device-code login against Floatplane's Keycloak
/// (<c>auth.floatplane.com</c>), the way Hydravion / Wasserflug / floatplane-downloader
/// log in. It needs a <c>client_id</c> registered by Floatplane; without one the server
/// answers <c>invalid_client</c>. Tokens are kept in the plugin configuration. DPoP-bound
/// clients are not supported (plain Bearer only).
/// </summary>
public class FloatplaneAuthService
{
    public const string Issuer = "https://auth.floatplane.com/realms/floatplane";
    private const string DeviceEndpoint = Issuer + "/protocol/openid-connect/auth/device";
    private const string TokenEndpoint = Issuer + "/protocol/openid-connect/token";
    private const string Scope = "openid profile email offline_access";

    private readonly IHttpClientFactory _httpClientFactory;
    private readonly ILogger<FloatplaneAuthService> _logger;
    private readonly SemaphoreSlim _refreshLock = new(1, 1);
    private PendingDeviceLogin? _pending;

    public FloatplaneAuthService(IHttpClientFactory httpClientFactory, ILogger<FloatplaneAuthService> logger)
    {
        _httpClientFactory = httpClientFactory;
        _logger = logger;
    }

    private static PluginConfiguration Config => Plugin.Instance?.Configuration ?? new PluginConfiguration();

    /// <summary>True when a refresh token is stored (OAuth login completed at some point).</summary>
    public static bool HasOAuthSession => !string.IsNullOrEmpty(Config.OAuthRefreshToken);

    /// <summary>Starts a device login: returns the code and URL the user must open.</summary>
    public async Task<DeviceLoginStart> StartDeviceLoginAsync(string clientId, CancellationToken ct)
    {
        var form = new Dictionary<string, string> { ["client_id"] = clientId, ["scope"] = Scope };
        using var response = await PostFormAsync(DeviceEndpoint, form, ct).ConfigureAwait(false);
        var json = await response.Content.ReadAsStringAsync(ct).ConfigureAwait(false);
        if (!response.IsSuccessStatusCode)
        {
            var err = Parse<OAuthError>(json);
            throw new FloatplaneApiException(response.StatusCode, err?.Error, err?.ErrorDescription ?? "Device authorization failed");
        }

        var start = Parse<DeviceLoginStart>(json) ?? throw new FloatplaneApiException(response.StatusCode, "parseError", "Unexpected device authorization response");
        _pending = new PendingDeviceLogin(clientId, start.DeviceCode, DateTimeOffset.UtcNow.AddSeconds(start.ExpiresIn), Math.Max(5, start.Interval));
        _logger.LogInformation("Floatplane device login started; user code {Code}", start.UserCode);
        return start;
    }

    /// <summary>One poll of the token endpoint; "pending" until the user has approved.</summary>
    public async Task<DeviceLoginStatus> PollDeviceLoginAsync(CancellationToken ct)
    {
        var pending = _pending;
        if (pending == null)
        {
            return new DeviceLoginStatus { State = "none", Message = "No login in progress" };
        }

        if (pending.ExpiresAt < DateTimeOffset.UtcNow)
        {
            _pending = null;
            return new DeviceLoginStatus { State = "expired", Message = "The code expired; start again" };
        }

        var form = new Dictionary<string, string>
        {
            ["grant_type"] = "urn:ietf:params:oauth:grant-type:device_code",
            ["client_id"] = pending.ClientId,
            ["device_code"] = pending.DeviceCode
        };
        using var response = await PostFormAsync(TokenEndpoint, form, ct).ConfigureAwait(false);
        var json = await response.Content.ReadAsStringAsync(ct).ConfigureAwait(false);
        if (response.IsSuccessStatusCode)
        {
            var tokens = Parse<TokenResponse>(json) ?? throw new FloatplaneApiException(response.StatusCode, "parseError", "Unexpected token response");
            StoreTokens(tokens, pending.ClientId);
            _pending = null;
            return new DeviceLoginStatus { State = "done", Message = "Logged in" };
        }

        var err = Parse<OAuthError>(json);
        switch (err?.Error)
        {
            case "authorization_pending":
                return new DeviceLoginStatus { State = "pending", Message = "Waiting for approval…", Interval = pending.Interval };
            case "slow_down":
                pending.Interval += 5;
                return new DeviceLoginStatus { State = "pending", Message = "Waiting (slower)…", Interval = pending.Interval };
            default:
                _pending = null;
                return new DeviceLoginStatus { State = "error", Message = err?.ErrorDescription ?? err?.Error ?? "Login failed" };
        }
    }

    /// <summary>Forgets the OAuth tokens (local only; Floatplane keeps the session until it expires).</summary>
    public static void Logout()
    {
        var cfg = Config;
        cfg.OAuthAccessToken = string.Empty;
        cfg.OAuthRefreshToken = string.Empty;
        cfg.OAuthAccessTokenExpiry = 0;
        Plugin.Instance?.SaveConfiguration();
    }

    /// <summary>
    /// Access token for API calls, refreshed when it has less than a minute left. Never
    /// refresh per request: ~40 refreshes in a row trip Cloudflare's 429 on auth.floatplane.com.
    /// </summary>
    public async Task<string?> GetAccessTokenAsync(CancellationToken ct)
    {
        var cfg = Config;
        if (string.IsNullOrEmpty(cfg.OAuthRefreshToken))
        {
            return null;
        }

        var expiry = DateTimeOffset.FromUnixTimeSeconds(cfg.OAuthAccessTokenExpiry);
        if (!string.IsNullOrEmpty(cfg.OAuthAccessToken) && expiry > DateTimeOffset.UtcNow.AddSeconds(60))
        {
            return cfg.OAuthAccessToken;
        }

        await _refreshLock.WaitAsync(ct).ConfigureAwait(false);
        try
        {
            cfg = Config;
            expiry = DateTimeOffset.FromUnixTimeSeconds(cfg.OAuthAccessTokenExpiry);
            if (!string.IsNullOrEmpty(cfg.OAuthAccessToken) && expiry > DateTimeOffset.UtcNow.AddSeconds(60))
            {
                return cfg.OAuthAccessToken;
            }

            var form = new Dictionary<string, string>
            {
                ["grant_type"] = "refresh_token",
                ["client_id"] = cfg.OAuthClientId,
                ["refresh_token"] = cfg.OAuthRefreshToken
            };
            using var response = await PostFormAsync(TokenEndpoint, form, ct).ConfigureAwait(false);
            var json = await response.Content.ReadAsStringAsync(ct).ConfigureAwait(false);
            if (!response.IsSuccessStatusCode)
            {
                var err = Parse<OAuthError>(json);
                _logger.LogWarning("Floatplane token refresh failed: {Error} {Description}", err?.Error, err?.ErrorDescription);
                if (err?.Error == "invalid_grant")
                {
                    Logout();
                }

                throw new FloatplaneAuthException(response.StatusCode, err?.Error ?? "refreshFailed", err?.ErrorDescription ?? "Token refresh failed");
            }

            var tokens = Parse<TokenResponse>(json) ?? throw new FloatplaneApiException(response.StatusCode, "parseError", "Unexpected token response");
            StoreTokens(tokens, cfg.OAuthClientId);
            return tokens.AccessToken;
        }
        finally
        {
            _refreshLock.Release();
        }
    }

    private static void StoreTokens(TokenResponse tokens, string clientId)
    {
        var cfg = Config;
        cfg.OAuthClientId = clientId;
        cfg.OAuthAccessToken = tokens.AccessToken ?? string.Empty;
        if (!string.IsNullOrEmpty(tokens.RefreshToken))
        {
            cfg.OAuthRefreshToken = tokens.RefreshToken;   // rotated on every refresh
        }

        cfg.OAuthAccessTokenExpiry = DateTimeOffset.UtcNow.AddSeconds(Math.Max(60, tokens.ExpiresIn)).ToUnixTimeSeconds();
        Plugin.Instance?.SaveConfiguration();
    }

    private async Task<HttpResponseMessage> PostFormAsync(string url, Dictionary<string, string> form, CancellationToken ct)
    {
        var client = _httpClientFactory.CreateClient(PluginServiceRegistrator.HttpClientName);
        using var request = new HttpRequestMessage(HttpMethod.Post, url) { Content = new FormUrlEncodedContent(form) };
        return await client.SendAsync(request, ct).ConfigureAwait(false);
    }

    private static T? Parse<T>(string json)
    {
        try
        {
            return JsonSerializer.Deserialize<T>(json);
        }
        catch (JsonException)
        {
            return default;
        }
    }

    private sealed class PendingDeviceLogin
    {
        public PendingDeviceLogin(string clientId, string deviceCode, DateTimeOffset expiresAt, int interval)
        {
            ClientId = clientId;
            DeviceCode = deviceCode;
            ExpiresAt = expiresAt;
            Interval = interval;
        }

        public string ClientId { get; }

        public string DeviceCode { get; }

        public DateTimeOffset ExpiresAt { get; }

        public int Interval { get; set; }
    }
}

public class DeviceLoginStart
{
    [JsonPropertyName("device_code")]
    public string DeviceCode { get; set; } = string.Empty;

    [JsonPropertyName("user_code")]
    public string UserCode { get; set; } = string.Empty;

    [JsonPropertyName("verification_uri")]
    public string VerificationUri { get; set; } = string.Empty;

    [JsonPropertyName("verification_uri_complete")]
    public string? VerificationUriComplete { get; set; }

    [JsonPropertyName("expires_in")]
    public int ExpiresIn { get; set; } = 600;

    [JsonPropertyName("interval")]
    public int Interval { get; set; } = 5;
}

public class DeviceLoginStatus
{
    public string State { get; set; } = string.Empty;

    public string? Message { get; set; }

    public int Interval { get; set; } = 5;
}

public class TokenResponse
{
    [JsonPropertyName("access_token")]
    public string? AccessToken { get; set; }

    [JsonPropertyName("refresh_token")]
    public string? RefreshToken { get; set; }

    [JsonPropertyName("expires_in")]
    public int ExpiresIn { get; set; }

    [JsonPropertyName("token_type")]
    public string? TokenType { get; set; }
}

public class OAuthError
{
    [JsonPropertyName("error")]
    public string? Error { get; set; }

    [JsonPropertyName("error_description")]
    public string? ErrorDescription { get; set; }
}